In the present study, NCEP ATP III defined MetS at baseline was associated with significantly higher risk of newly onset CVD. Similarly, IDF defined MetS correlated with newly onset Stroke among elderly from rural China. As for individual metabolic components, only abdominal obesity defined by NCEP ATP III was fond to be correlated with newly onset Stroke. All the predictive effects of MetS or metabolic components on newly onset CHD, Stroke or CVD was statistically significant among female but not male.
During the past decades, with the rapid development of economic growth, changes in lifestyle and longer life expectancy, geriatric population increase worldwide. Together with the aging population, is that age-related metabolic disorders, like hypertension, diabetes, obesity and dyslipidemia which gradually became more prevalent. The high rates of cardiometabolic risk factors resulted in dramatically increased cardiovascular and cerebrovascular problems with a high morbidity and mortality in elderly subjects. According to the WHO definition, the prevalence of MetS in elderly population varied from 11–43% (median 21%), and 23–55% (median 31%) while according to NCEP ATP III criteria [7, 12]. Obesity and hypertension are the most prevalent individual components among them. During the past decades, cardiometabolic disorders gradually decreased in developed countries due to the effective propagation, prevention and treatment. However, they still occurred frequently in rural or developing areas. Our previous data showed that during 2012–2013 year, the prevalence of hypertension (74.8%), diabetes (14.9%), dyslipidemia (67.4%), obesity (39.9%), stroke (18.9%) and hyperuricemia (13.1%) among elderly were significantly high in rural China . In the present study, the MetS by IDF criteria was 35.5% and by NCEP ATP III criteria was 28.4% closed to the data from urban cities like Beijing [MetS by NCEP criteria was 30.5% (17.6% in men, 39.2% in women) ; IDF definition was 46.3% (34.8% in men, 54.1% in women)] . Due to the high prevalence of MetS among rural elderly subjects, it is necessary to estimate the possible effect of MetS on the newly onset CHD, stork, and CVD in order to better preventing and controlling cardiovascular mortality and morbidity.
There were already many previous studies, intending to estimate the relationship between MetS and CHD or stroke, coming out with inconsistent results. One cross-sectional study enrolled 4,748 residents (aged ≥ 30 years) in rural China during 2006 to 2007, concluded that NCEP-ATP III defined MetS was more suitable than IDF and Chinses Diabetes Society criteria for screening and estimating the risk of CHD and Stroke from MetS, especially in men . Similarly, elderly subjects from Beijing with MetS had significantly higher risk of CHD (NCEP ATP III criteria, OR: 1.43; IDF criteria, OR: 1.69), Stroke (NCEP ATP III criteria, OR: 1.45; IDF criteria, OR: 1.58), PAD (NCEP ATP III criteria, OR: 1.47; IDF criteria, OR: 1.42) and CVD (NCEP ATP III criteria, OR: 1.50; IDF criteria, OR: 1.73) . However, in the Prospective study of Pravastatin in the Elderly at Risk (PROSPER) and British Regional Heart Study (BRHS) studies, weak or no association between MetS and vascular risk in elderly subjects were found using NCEP ATP III definition . Elderly subjects usually accompany with many cardiovascular risk or established coronary artery diseases. Therefore, when we evaluated the association between cardiovascular risk factors and CVD, we should take into account about this. Ana Teresa Timóteo and colleagues reported that among subjects (a mean age of 65 ± 9 year) with high cardiovascular risk, the presence of MS at baseline was not associated with cerebral or cardiac events in long-term follow-up . As far as we knew, most of the previous studies estimated relationship between MetS and CVD were cross-sectional analysis which restricted their accuracy. As a prospective study, we found that MetS defined by NCEP ATP III and IDF at baseline was correlated with newly onset CVD and stroke respectively in women but not men which help to confirm the effect of MetS on CHD, stroke or CVD. This results were coincidence with previous study which suggested that the association between MetS and CVD were more pronounced when the NCEP ATP III and AHA/NHLBI criteria were implemented compared with IDF definition . However, study held in China concluded that IDF defined MetS was more strongly associated with CHD than the NCEP or revised NCEP defined MetS, but weakly or not associated with stroke which was inconsistent with our results . In our study, abdominal obesity at baseline increased the newly onset stroke in female elderly but not male. This was consistent with many previous studies. Data from the National Stroke Screening Survey in 2012 and the 2010 Chinese population from sixth National Census of Populations showed that compared to male elderly, female elder subjects with stroke were more likely to have obesity, diabetes, elevated LDL-C and atrial fibrillation . It might partially due to the significantly lower rate of abdominal obesity in male compared to female (2.9% vs. 29.4%, P < 0.001) in the present study which lead to the predictive effect of MetS on newly onset Stroke become insignificant.
One interesting finding in the present study was that the predictive effect of MetS on newly onset CHD, Stroke or CVD was significant in female elderly but not male elderly. First, it might be due to the gender discrepancy in the prevalence of MetS in elderly subjects. Trevisan et al reported that subjects aged ≥ 50 years, women had significantly higher prevalence of MetS than men . Similarly, study held in USA elderly aged ≥ 70 years showed that MetS (NCEP ATP III) was more prevalent among women than men . MetS prevalence showed gender discrepancy in elderly female than in male although general epidemiological studies with adults have found higher prevalence rates of MetS in men than in women . Women had significantly higher rate of MetS at baseline which might resulted in a significant predictive effect of MetS on newly onset CVD in future. Second, except for baseline MetS, there are many possible confounders that have been analysis in our model which might cause the association between MetS and CVD became insignificant. In the present study, after adjusted for possible confounders, MetS (OR: 1.33), female gender (OR: 1.42), increasing age (OR: 1.04), and family history of hypertension (OR: 1.54) were associated with increased risk of newly onset CVD. We further analyzed the characters of female of male participants separately and found that female elderly had significantly higher rate of family history of hypertension than male elderly (19.7% vs. 16.2%, P = 0.012). Therefore, it might make the association between MetS and CVD more pronounced in female elderly.